From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262375AbTLNUaq (ORCPT ); Sun, 14 Dec 2003 15:30:46 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262397AbTLNUap (ORCPT ); Sun, 14 Dec 2003 15:30:45 -0500 Received: from roc-24-93-20-125.rochester.rr.com ([24.93.20.125]:54772 "EHLO mail.kroptech.com") by vger.kernel.org with ESMTP id S262375AbTLNUao (ORCPT ); Sun, 14 Dec 2003 15:30:44 -0500 Date: Sun, 14 Dec 2003 15:35:04 -0500 From: Adam Kropelin To: Nathan Fredrickson <8nrf@qlink.queensu.ca> Cc: Con Kolivas , Linux Kernel Mailing List , Nick Piggin , Ingo Molnar , sam@mars.ravnborg.org Subject: Re: HT schedulers' performance on single HT processor Message-ID: <20031214153504.A6795@mail.kroptech.com> References: <200312130157.36843.kernel@kolivas.org> <1071431363.19011.64.camel@rocky> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5.1i In-Reply-To: <1071431363.19011.64.camel@rocky>; from 8nrf@qlink.queensu.ca on Sun, Dec 14, 2003 at 02:49:24PM -0500 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Dec 14, 2003 at 02:49:24PM -0500, Nathan Fredrickson wrote: > Same table as above normalized to the j=1 uniproc case to make > comparisons easier. Lower is still better. > > j = 1 2 3 4 8 > 1phys (uniproc) 1.00 1.00 1.00 1.00 1.00 > 1phys w/HT 1.02 1.02 0.87 0.87 0.87 > 1phys w/HT (w26) 1.02 1.02 0.87 0.87 0.88 > 1phys w/HT (C1) 1.03 1.02 0.88 0.88 0.88 > 2phys 1.00 1.00 0.53 0.53 0.53 ^^^^^ ^^^^ Ummm... > 2phys w/HT 1.01 1.01 0.64 0.50 0.48 > 2phys w/HT (w26) 1.02 1.01 0.55 0.49 0.47 > 2phys w/HT (C1) 1.02 1.01 0.53 0.50 0.48 > There was not much benefit from either HT or SMP with j=2. Maximum > speedup was not realized until j=3 for one physical processor and j=5 > for 2 physical processors. This is mighty suspicious. With -j2 did you check to see that there were indeed two parallel gcc's running? Since -test6 I've found that -j2 only results in a single gcc instance. I've seen this on both an old hacked-up RH 7.3 installation and a brand new RH 9 + updates installation. > This suggests that j should be set to at least the number of logical > processors + 1. Since -test6 I've found this to be the case for kernel builds, yes. But I don't think it has anything to do with the scheduler or HT vs SMP platforms. --Adam